Method of Detecting Pilot Tones in a Noisy Signal

1. A method for detecting the presence of a pilot tone, whose characteristics are known, in a signal, the method comprising the steps of sampling the signal, and recording the values of the samples from a desired recording length, wherein the method further comprises the steps of calculating one spectral component of Fourier transform for the values of the samples, and comparing the result of the calculation to at least one predetermined value for deciding whether the pilot tone is present or not.

2. A method according to claim 1 , wherein the sampling step includes the step of selecting a suitable sample rate depending on the features of the pilot tone, the signal, and the sampling step.

3. A method according to claim 2 , wherein the selecting step the sample rate is chosen to be four times the frequency of the pilot tone.

4. A method according to claim 3 , wherein the calculating step comprises the step of accumulating sums of the values.

5. A method according to claim 2 , wherein when selecting the sample rate to be different than four times the frequency of the pilot tone, a step of setting coefficients for the calculating step is between the step of recording the values and the step of calculating one spectral component of Fourier transform.

6. A method according to claim 5 , wherein the calculating step comprises the steps of accumulating sums of the values, multiplying the sums by the coefficients, and adding multiplied sums together.

7. A method according to claim 1 , further comprising integrating the signal when recording the values for the samples.

8. A method according to claim 1 , further comprising reducing crosstalk between pilot tones when several signals with pilot tones exist, by equally spacing frequencies of pilot tones and selecting a specific measurement time for the pilot tones to ensure the reduction of crosstalk.

9. A method according to claim 8 , further comprising selecting an equal measurement time for the pilot tones to ensure the reduction of crosstalk.

10. A method according to claim 1 , further comprising reducing crosstalk between pilot tones when several signals with pilot tones exist, by arranging the pilot tones in pairs with a pair-specific frequency difference and a pair-specific measurement time.

11. A method according to claim 1 , further comprising reducing crosstalk between pilot tones when several signals with pilot tones exist, by arranging the pilot tones in pairs with a specific frequency difference and a specific measurement time, both being equal to all pairs.

12. A method for measuring a pilot tone, which pilot tone's characteristics are known, in a signal, the method comprising the steps of sampling the signal, and recording the values of the samples from a desired recording length, wherein the method further comprises the steps of calculating one spectral component of Fourier transform for the values of the samples, and using the calculated spectral component as a measure of the amplitude of the pilot tone.

13. A method according to claim 12 , wherein the sampling step includes the step of selecting a suitable sample rate depending on the features of the pilot tone, the signal, and the sampling step.

14. A method according to claim 13 , wherein in the selecting step the sample rate is chosen to be four times the frequency of the pilot tone.

15. A method according to claim 14 , wherein the calculating step comprises the step of accumulating sums of the values.

16. A method according to claim 13 , wherein when selecting the sample rate to be different than four times the frequency of the pilot tone, a step of setting coefficients for the calculating step is between the step of recording the values and the step of calculating one spectral component of Fourier transform.

17. A method according to claim 16 , wherein the calculating step comprises the steps of accumulating sums of the values, multiplying the sums by the coefficients, and adding multiplied sums together.

18. A method according to claim 12 , further comprising integrating the signal when recording the values for the samples.

19. A method according to claim 12 , further comprising reducing crosstalk between pilot tones when several signals with pilot tones exist, by equally spacing frequencies of pilot tones and selecting a specific measurement time for the pilot tones to ensure the reduction of crosstalk.

20. A method according to claim 19 , further comprising selecting an equal measurement time for the pilot tones to ensure the reduction crosstalk.

21. A method according to claim 12 , further comprising reducing crosstalk between pilot tones when several signals with pilot tones exist, by arranging the pilot tones in pairs with a pair-specific frequency difference and a pair-specific measurement time.

22. A method according to claim 12 , further comprising reducing crosstalk between pilot tones when several signals with pilot tones exist, by arranging the pilot tones in pairs with a specific frequency difference and a specific measurement time, both being equal to all pairs.

23. An arrangement for detecting the presence of a pilot tone, whose characteristics are known, in a signal, the arrangement comprising sampling means for sampling the signal, and recording means for recording the values of the samples, wherein the arrangement further comprises means for calculating one spectral component of Fourier transform for the values of the samples, means for comparing the result of the calculation to at least one predetermined value for deciding whether the pilot tone is present or not.

24. An arrangement according to claim 23 , wherein the arrangement further comprises means of setting coefficients of the values of the samples.

25. An arrangement according to claim 23 , wherein the recording means further comprises means of selecting a recording length.

26. An arrangement for measuring a pilot tone, which pilot tone's characteristics are known, in a signal, the arrangement comprising sampling means for sampling the signal, and recording means for recording the values of the samples, wherein the arrangement further comprises first means for calculating one spectral component of Fourier transform for the values of the samples, second means, respective to first means, for recording the value of the calculated spectral component as a measure of the amplitude of the pilot tone.

27. An arrangement according to claim 26 , wherein the arrangement further comprises means of setting coefficients of the values of the samples.

28. An arrangement according to claim 26 , wherein the recording means further comprises means of selecting a recording length.